This invention relates to pressure control apparatus and, more particularly, to pressure control apparatus including a pressure control valve for a torque-transmitting mechanism.
Automatic shifting power transmissions include a plurality of torque-transmitting mechanisms such as friction clutches and brakes. These clutches and brakes are generally fluid-operated mechanisms, which require a fluid pressure control to complete engagement and disengagement of the torque-transmitting mechanism. These mechanisms and their structure are well known in the art, as are many pressure controls for establishing the engagement and disengagement of the torque-transmitting mechanism.
In many of the current transmissions, it is desirable to control the engagement pressure of a torque-transmitting mechanism at an increasing rate or a ramp rate during engagement of the torque-transmitting mechanism and to increase the pressure to a maximum value when the torque-transmitting mechanism has been fully engaged. The ramp control pressure is important in that it controls the frictional engagement at low levels during ratio interchanges when one torque-transmitting mechanism is being engaged and another is being disengaged.
Many of the prior art controls for torque-transmitting mechanisms incorporate variable gain valves wherein a first control rate is used during a portion of the engagement and a second control rate is used during the remainder of the control pressure engagement. Many of these valves incorporate differential areas formed on a valve spool to provide the different gain rates that are required for overall control of the friction device.
Also, many of the prior art control mechanisms employ a solenoid signal, which is controlled at pressure levels to provide the required gain at the torque-transmitting mechanism control member. These control signals or solenoids might be a variable bleed solenoid or a pulse-width-modulated solenoid, both of which are well known to those skilled in the art. These solenoid pressure controls are generally established by an electronic control module, which includes a programmable digital computer, which contains the necessary information for controlling the torque-transmitting mechanism pressure throughout a shift interchange or a ratio interchange as well as controlling the pressure after the interchange is completed. In many instances, the control pressure of the solenoid valve is utilized to provide the full range of torque-transmitting mechanism pressure required for both regulation during ratio interchanges and full engagement.
It is an object of the present invention to provide an improved pressure control apparatus for a torque-transmitting mechanism.
In one aspect of the present invention, the pressure control apparatus includes a valve spool slidably disposed in a valve bore and operable to provide control pressure to a torque-transmitting mechanism.
In another aspect of the present invention, the valve spool is operable to distribute a system pressure to the torque-transmitting mechanism as well as to a feedback area on the valve spool to control the gain or the pressure rise at the torque-transmitting mechanism.
In still another aspect of the present invention, the spool valve is controlled by a variable pressure signal from a solenoid source and the feedback pressure is operable to counteract a portion of the control signal thereby controlling the rate of pressure rise at the torque-transmitting mechanism.
In yet still another aspect of the present invention, a boost valve is incorporated internally of the spool valve to provide for a high pressure output to the torque-transmitting mechanism.
In a further aspect of the present invention, the opening and closing of the boost valve is controlled by the variable pressure signal from the solenoid valve, such that when the solenoid valve reaches a maximum or a predetermined pressure, the boost valve is operable.
In a yet further aspect of the present invention, the boost valve when in an operable position decreases or eliminates the feedback pressure on the valve spool thereby causing a maximum output pressure for the torque-transmitting mechanism.
In a still further aspect of the present invention, the boost valve incorporates a ball valve, which is responsive to the variable solenoid pressure to permit fluid flow to the feedback differential area when the boost is not required and to exhaust the feedback area when boost is required.